<!DOCTYPE html>
<html>
<head lang="en">
    <meta charset="UTF-8">
    <title></title>
    <script src="Itcast.js"></script>
</head>
<body>
<div>1</div>
<div>2</div>
<div>3</div>
<div>4</div>
<script>


    var Iobj = I( 'div' );

    var first=Iobj.first();




</script>
</body>
</html>